PD/PI: Takemaru, Ken-Ichi Title: Chibby and Its Associated Proteins in Ciliated Cell Differentiation PROJECT SUMMARY Motile multicilia are abundant in the respiratory tract and beat synchronously in waves to propel inhaled debris and pathogens entrapped in mucus to the pharynx. This provides an important innate defense mechanism against respiratory infections. Multicilia are usually found as clusters of 100 to 300 on the apical surface of a ciliated cell in the respiratory epithelium. Dysfunction of multicilia has been linked to various pulmonary diseases such as asthma, chronic obstructive pulmonary disease (COPD), and primary ciliary dyskinesia (PCD). Despite their clinical importance, little is known about the key molecules and mechanisms that govern multiciliogenesis and ciliated cell differentiation. Therefore, understanding these fundamental biological phenomena is crucial for developing novel therapeutic strategies for the prevention and treatment of cilia-related pulmonary disorders. We previously demonstrated that the small coiled-coil protein Chibby (Cby) localizes to the basal body (BB) of cilia and plays an essential role in ciliogenesis and differentiation of airway ciliated cells in mice. More recently, we reported that during early stages of ciliated cell differentiation, Cby facilitates efficient docking of BBs to the apical cell membrane via formation of membranous structures, called ciliary vesicles (CVs). Mechanistically, Cby is recruited to the BBs through protein-protein interactions with the ciliopathy-associated protein CEP164. Cby then interacts with the membrane trafficking machinery component Rabin8, a guanine nucleotide exchange factor (GEF) for the small GTPase Rab8, to promote recruitment of Rab8 and CV assembly. Cby may also play a role in biogenesis and homeostasis of the ciliary membrane (CM) as it continues to localize at the base of elongating and mature cilia. However, the molecular components and mechanisms of assembly of CVs and CMs and BB docking remain poorly understood. For this competing R01 renewal proposal, we have established a conditional CEP164-KO mouse model to study its function during ciliated cell differentiation in vivo. Furthermore, we have successfully identified bona fide Cby-interacting proteins, named FAM92A and FAM92B, which harbor a putative membrane-binding Bin/Amphiphysin/Rvs (BAR) domain. We propose to investigate their molecular roles in differentiation of airway ciliated cells. The overall goal of this proposal is to elucidate the roles of Cby, CEP164, and FAM92 proteins in CV formation, BB docking, and ciliated cell differentiation with the following Specific Aims: Specific Aim 1. Investigate the role of CEP164 in ciliated cell differentiation; Specific Aim 2. Study the roles of FAM92A and FAM92B in ciliogenesis and ciliated cell differentiation; Specific Aim 3. Elucidate the membrane-binding and curving properties of FAM92A, FAM92B, and Cby. We anticipate that these experiments will contribute to a fundamental understanding of the molecular and cellular mechanisms of ciliogenesis and ciliated cell differentiation.